Test for object identity should be is¶
Testing the identity of two objects can be achieved in python with a special operator called is.
Most prominently it is used to check whether an variable points to None.
But the operator can examine any kind of identity.
This often leads to confusion because equality of two different objects will return False.
Anti-pattern¶
a = range(10)
b = range(10)
print((a is b))
This code snippet will print False even though a and b have equal values.
This can occur because a and b are references that point to different objects which happen to have the same value.
To verify the equality of two variables the == operator should be used.
Best practice¶
Only use the is operator if you want to check the exact identity of two references.
some_list = None
if some_list is None:
do_somthing_with_the_list()